Turnbull could expand cabinet for new Nationals deputy

Nationals MPs are pushing for Malcolm Turnbull to expand his cabinet to 22 people after Nationals backbencher Bridget McKenzie was promoted to the junior Coalition party's deputy leadership on Thursday.

And Peter Dutton's new super portfolio of Home Affairs, which will include police and security agencies including spy agency ASIO, the Federal Police, Border Force and the Australian Criminal Intelligence Commission will begin operating by the end of the year, about six months ahead of schedule.

The new Home Affairs portfolio will be similar to the British Home Office and function as a central department that provides strategic planning, co-ordination and other support to independent security and law enforcement agencies.

It will be led by Mike Pezzullo and the decision to move the spy agency from being the responsibility of Attorney-General George Brandis and to the new portfolio represents a win for Mr Dutton; however, some legislation will need to be passed to move ASIO over to the new department.

The futures of Senator Brandis and fellow cabinet minister Arthur Sinodinos have been the subject of months of speculation; Senator Brandis is the hot tip to take the High Commissioner's job in London - though this week he said it was his intention to remain in Parliament - while Senator Sinodinos is battling cancer.

Deputy Liberal leader Julie Bishop is a strong supporter of Senator Brandis remaining in his post.

The week before Christmas - after the Bennelong byelection on December 16, and the mid-year economic update on December 18 - is firming as the most likely date for the prime minister to reshuffle his front bench.

Senator McKenzie was a surprise pick for the deputy leader's job; she beat out Resources Minister Matt Canavan and junior ministers Michael McCormack and Keith Pitt for the deputy's job; Victoria, NSW and NT members locked in behind her to secure the win.

Under the formula used to determine the number of Liberals and Nationals in the cabinet, the junior Coalition partner is entitled to only four cabinet posts in a 20, 21 or 22 member cabinet. At present there are 21 cabinet ministers.

Nationals leader Barnaby Joyce and Senator McKenzie are guaranteed a spot because of their leadership roles, which would mean one of the Nationals' other three cabinet ministers - Matt Canavan, Darren Chester or Nigel Scullion - would have to be demoted.

But the demotion of a Nationals cabinet minister would likely cause a massive political headache for the Prime Minister - who was last week forced to order a royal commission into the banks because of a back bench revolt - and the Nationals are hopeful Mr Turnbull will accede to allocating them five cabinet posts.

Multiple MPs, from across the backbench to the cabinet, confirmed to Fairfax Media that five cabinet ministers was the most likely outcome.

Mr Joyce declined to comment on Thursday whether he would be asking for the Nationals to keep five cabinet posts.

"All these things are part of the discussion, I'm looking forward to having a discussion with the Prime Minister at a later stage when the Prime Minister chooses to have a reshuffle," he told Sky News.

Senator McKenzie would not name any portfolios she wanted, only that she wanted something that lets her "get out on the ground in the regions and deliver tangible benefits".

"I'll hopefully get a portfolio that will allow me to deliver substantial outcome for them [regional Australians]."

The gun-loving Senator McKenzie's promotion came as Federal Parliament was poised to finally legalised same-sex marriage - a reform she opposed despite having a gay younger brother, Alastair.

The Nationals leader once described Senator McKenzie as a "flash bit of kit" during a late night Senate debate, prompting accusations he was drunk in the chamber - and an eventual apology.